Hey Jeet02,
Yes, this is true that a girl who is very interested will sometimes take the initiative to select a later date if you have chosen one that legitimately does not work for her. However, all you are doing by picking a specific date and time is restricting the subset of girls who are on the edge about you and not willing to suggest a later date -- sometimes out of fear of coming across as "too needy."
There are a couple of other issues with selecting a date and time as well, especially if it is that night or the next night that you are suggesting. A well-socialized girl that gets a text saying something along the lines of, "hey, let's get together tonight!" will immediately wonder how many other girls you've sent that text to that night. Is this just a booty call? Are you just bored? Why are you so eager to hang out tonight? Keep in mind that there is nothing leading or powerful about a text message. It doesn't take much "manliness" to send a text message to a girl, so instead of trying to lead her in texting, you should be just focusing on trying to get her out so you can lead her in person.
Telling a girl that you want to know her schedule implicitly lets her know that you are legitimately interested in getting together with her because you want to know when she is free, even if it is later in the week.
Another issue with asking a girl to come over at a specific time is that she might feel like she just won't be ready yet. Sometimes this can be as simple as her wanting to get her nails or her hair done... or even "shaving" certain parts of her body. Girls do a lot to get ready for a promising date!
Once you've slept with a girl already, most of these rules go out the window. But if you are going for a first date, it's best to give her every opportunity you can to see you.
This is my two cents.
- Franco